1. Field of the Invention
The present invention relates to a process for the preparation of a dispersion of a water-soluble cationic polymer which is useful as a flocculant or dehydrating agent for waste water disposal or as a papermakers chemical.
2. Description of the Prior Art
Known processes for the preparation of a water-soluble cationic polymer which is useful as a flocculant for waste water disposal or as a papermakers chemical include standing polymerization in an aqueous solution, water-in-oil emulsion polymerization (see, for example, Japanese Patent Laid-Open No. 102388/1979), suspension polymerization in a hydrophobic solvent (see, for example, Japanese Patent Laid-Open No. 69196/1979) and so on.
Further, there has been disclosed a process for preparing a water-soluble, nonionic or anionic polymer by precipitation polymerization in an aqueous solution of ammonium sulfate (see, for example, Japanese Patent Laid-Open No. 70489/1975).
Also there have been disclosed a process for carrying out the polymerization in an aqueous solution of a salt in the presence of a polyhydric alcohol (see, for example, Japanese Patent Laid-Open No. 20502/1987) and a process for carrying out the polymerization in an aqueous solution of a salt in the presence of a polyelectrolyte as a dispersant (see, for example, Japanese Patent Laid-Open Nos. 123610/1986 and 20511/1987).
The standing polymerization in an aqueous solution, however, must be carried out with a monomer concentration of at least 10% by weight in order to obtain a high-molecular weight polymer. Therefor, the product is given in a state of water-containing gel, so that it is difficult to dissolve the product as such. Accordingly, the product must be put on the market in a state of a low-concentration solution obtained by further diluting a product or must be dried and powdered. With respect to the low-concentration solution, the transportion cost is disadvantageously enhanced, while with respect to the powdering of the product, much heat energy is necessitated for drying the product and the product disadvantageously causes three-dimensional crosslinking by heating to insolubilize a part thereof.
Meanwhile, the water-in-oil emulsion polymerization has a problem that a flammable and valuable organic solvent is consumed wastefully. Further, the suspension polymerization in a hydrophobic solvent has a problem that the production equipment costs a great deal, because a flammable material such as cyclohexane or toluene is used. The precipitation polymerization in an aqueous solution of ammonium sulfate has a problem that the formed polymers adhere to each other to form big lumps, resulting in difficult handling, though it is a preferable method with a low cost of equipment. Furthermore, it is difficult to prepare a polymer in a state of fine particle by using a conventional dispersant.